Photosynthetic carbon metabolism in isolated pea chloroplasts: metabolite levels and enzyme activities

We report here that enzyme activation precedes the rise in metabolite levels, which appear to limit photosynthetic CO2 fixation during induction in pea leaf chloroplasts. Therefore light activation may be required for the build-up of photosynthetic intermediates and hence for photosynthesis in isolated chloroplasts. Analysis of metabolite levels and the known kinetic properties of the chloroplast enzymes indicates that the reductive pentose phosphate cycle is subject to control which fluctuates between several points during induction and when CO2 fixation is maximal. The transketolase-aldolase-catalyzed reactions around sedoheptulose-biphosphatase appear to provide a simple and effective primary control for photosynthetic CO2 fixation. When substrate levels and enzyme active site concentrations are taken into account, there is insufficient glyceraldehyde 3-phosphate dehydrogenase, aldolase, and transketolase activity to support photosynthetic CO2 fixation at observed rates. These results suggest that there may be direct transfer of glyceraldehyde 3-phosphate among these enzymes in the pea chloroplast.     

Photosynthetic performance in wild emmer wheat,Triticum dicoccoides: ecological and genetic predictability

Summary In a twin study, we have shown that wild emmer wheat, Triticum dicoccoides, the progenitor of all cultivated wheats, harbours important genetic variation (Vg) in photosynthetic characteristics. This Vg resides within and between populations and ecogeographical regions in Israel, which is the center of origin and diversity of wild emmer wheat. Here we analyzed, by univariate and multivariate methods, the significant differentiation of variation in photosynthetic characteristics of 107 genotypes from 27 populations of wild emmer in Israel, distributed in three ecogeographical regions including central, xeric (northern cold and eastern warm) marginal, and mesic (western) marginal populations. The highest photosynthetic efficiency was displayed by populations of the xeric marginal region, but most variation for photosynthetic capacity occurs between accessions within ecogeographical regions and populations. Genotypes and populations of T. dicoccoides having high photosynthetic capacity can be identified by climatic factors and isozyme markers. The identification by genetic markers, if substantiated by testcrosses, can facilitate the maximization of conservation, in situ or ex situ, and utilization of these photosynthetic genetic resources for improvement of hexaploid wheat (T. aestivum).     

Phospholipid metabolism in cotyledons of wild and cultivated peas

The amount of phospholipids in the membrane fractions of the endoplasmic reticulum (ER) and plasma membrane of cotyledons of Pisum sativum and P. elatius was followed during germination. Incorporation of [¹⁴C-methyl]choline into the ER and the plasma membrane was followed as well as [U-¹⁴C]glycerol into the ER. The pool size of endogenous choline was determined and found to be much greater in the wild pea and to increase early in germination. In both species membranes are synthesized in large quantities early in germination and both turnover and synthesis of the backbone and the phosphatidyl tail occur throughout 48 hr of germination. In P. sativum incorporation peaks earlier than in P. elatius and degradation also begins earlier than in P. elatius. This is consistent with the general behaviour of the two species.     

Photosynthetic carbon metabolism in seagrasses C-labeling evidence for the c(3) pathway

The δ¹³C values of several seagrasses were considerably less negative than those of terrestrial C₃ plants and tended toward those of terrestrial C₄ plants. However, for Thalassia hemprichii (Ehrenb.) Aschers and Halophila spinulosa (R. Br.) Aschers, phosphoglycerate and other C₃ cycle intermediates predominated among the early labeled products of photosynthesis in ¹⁴C-labeled seawater (more than 90% at the earliest times) and the labeling pattern at longer times was brought about by the operation of the C₃ pathway. Malate and aspartate together accounted for only a minor fraction of the total fixed label at all times and the kinetic data of this labeling were not at all consistent with these compounds being early intermediates in seagrass photosynthesis. Pulse-chase ¹⁴C-labeling studies further substantiated these conclusions. Significant labeling of photorespiratory intermediates was observed in all experiments. The kinetics of total fixation of label during some steady-state and pulse-chase experiments suggested that there may be an intermediate pool of inorganic carbon of variable size closely associated with the leaves, either externally or internally. Such a pool may be one cause for the C₄-like carbon isotope ratios of seagrasses.     

Phylogeny of the a genomes of wild and cultivated wheat species

Diploid species of the genus Triticum L. are its most ancient representatives and have the A genome, which was more recently inherited by all polyploid species. Studies of the phylogenetic relationships among diploid and polyploid wheat species help to identify the donors of elementary genomes and to examine the species specificity of genomes. In this study, molecular analysis of the variable sequences of three nuclear genes (Acc-1, Pgk-1, and Vrn-1) was performed for wild and cultivated wheat species, including both diploids and polyploids. Based on the sequence variations found in the genes, clear differences were observed among elementary genomes, but almost no polymorphism was detected within each genome in polyploids. At the same time, the regions of the three genes proved to be rather heterogeneous in the diploid species Triticum boeoticum Boiss., T. urartu Thum. ex Gandil., and T. monococcum L., thus representing mixed populations. A genome variant identical to the A genome of polyploid species was observed only in T. urartu. Species-specific molecular markers discriminating the diploid species were not found. Analysis of the inheritance of morphological characters also failed to identify a species-specific character for the three diploid wheat species apart from the hairy leaf blade type, described previously.     

Effects of aminoacetonitrile on net photosynthesis, ribulose-1,5-bisphosphate levels, and glycolate pathway intermediates

The effects of aminoacetonitrile (a competitive inhibitor of glycine oxidation) on net photosynthesis, glycolate pathway intermediates, and ribulose-1,5-bisphosphate (RuBP) levels have been investigated at different O₂ and CO₂ concentrations with soybean (Glycine max)[L] Merr. cv Pioneer 1677) leaf discs floated on 25 millimolar aminoacetonitrile (AAN) for 50 minutes prior to assay.

At 2% O₂ and 200 or 330 microliters per liter CO₂, the inhibitor had no effect on the rate of net photosynthesis and RuBP levels when compared with the control levels. At 11% to 60% O₂, AAN caused a decrease in net photosynthesis in addition to the inhibition by O₂. This extra inhibition ranged from 22% to 59% depending on the O₂ and CO₂ concentrations. The levels of RuBP, however, were 1.3 to 2.7 times higher than in the control plants at the same O₂ concentrations. At 40% O₂ and 200 microliters per liter CO₂, the inhibitor caused a 6-fold increase in glycine and more than 2-fold increase in glyoxylate levels, whereas those of glycolate decreased by approximately one-half.

The decrease in net photosynthesis observed with AAN is not the result of the depletion of the RuBP pool due to the lack of recycling of carbon from the glycolate pathway to the Calvin cycle. The higher levels of RuBP caused by AAN in photorespiratory conditions, suggest that RuBP carboxylase was inhibited. Glyoxylate could be a possible candidate for the inhibition of the enzyme but what is known so far about its inhibitory properties in vitro may not fit the existing in vivo conditions. An alternative explanation for the inhibition is proposed.

     

Comparative assessment of genetic diversity in wild and primitive cultivated barley in a center of diversity

Wild barley (Hordeum spontaneum K.) and indigenous primitive varieties of cultivated barley (Hordeum vulgare L.), collected from 43 locations in four eastern Mediterranean countries, Jordan, Syria, Turkey and Greece, were electrophoretically assayed for genetic diversity at 16 isozyme loci. Contrary to a common impression, cultivated barley populations were found to maintain a level of diversity similar to that in its wild progenitor species. Apportionment of overall diversity in the region showed that in cultivated barley within-populations diversity was of higher magnitude than the between-populations component. Neighboring populations of wild and cultivated barleys showed high degree of genetic identity. Groups of 3 or 4 isozyme loci were analyzed to detect associations among loci. Multilocus associations of varying order were detected for all three groups chosen for the analysis. Some of the association terms differed between the two species in the region. Although there was no clear evidence for decrease in diversity attributable to the domestication of barley in the region, there was an indication of different multilocus organizations in the two closely related species.     

Photosynthetic intermediates, the warburg effect, and glycolate synthesis in isolated spinach chloroplasts

Increasing levels of CO(2) have been shown to stimulate the rate of photosynthesis, eliminate the oxygen inhibition of photosynthesis (Warburg effect), and decrease glycolate formation in isolated spinach chloroplasts. Ribose 5-phosphate and fructose 1,6-diphosphate at concentrations of 5 to 10 mum also stimulate the rate of plastid photosynthesis and eliminate the Warburg effect. In contrast to the effect of high CO(2) levels, these sugar phosphates have little effect on glycolate formation. Evidence is presented to show that the level of intermediates of the photosynthetic carbon reduction cycle may influence the Warburg effect in vivo. It is postulated that the formation of glycolate is not the causal factor of the Warburg effect.     

Photosynthetic characteristics of three ploidy levels of Allium oleraceum L. (Amaryllidaceae) differing in ecological amplitude

To elucidate the mechanisms of the adaptive advantages of polyploidy, there is a need to identify physiological traits that participate in the success of polyploids. We studied selected photosynthetic characteristics, stomatal density, and specific leaf area of three ploidy levels (2n = 4x, 5x, 6x) of the geophyte Allium oleraceum that partially differ in their ecological niches. Although the cytotypes were on average similar with regard to most of the measured photosynthetic traits, the hexaploids showed more rapid initial photosynthetic induction and a tendency for a higher maximum photosynthetic rate per unit area. The stomatal density was not affected by ploidy, though the specific leaf area was reduced for the hexaploids compared to the other cytotypes. A lower intracytotype variation was found for most of the studied photosynthetic and anatomical traits for the hexaploids compared to the large variation found within other cytotypes. A comparison of the photosynthetic traits between the cytotypes showed that the ecological differentiation between cytotypes is only weakly related to the characteristics of their photosynthetic apparatus. However, contrasting ranges of variability in the measured traits between the cytotypes can be related to previously observed differences between cytotypes with regard to the ranges of intracytotype genetic variation, genome size variation, and niche breadth. A higher variability of photosynthetic traits in tetraploids and pentaploids may be related to the existence of a spectrum of types adapted to different environmental conditions. Hexaploids may represent a recently formed cytotype adapted to open environmental conditions.     

Divergent regulation of terpenoid metabolism in the trichomes of wild and cultivated tomato species

The diversification of chemical production in glandular trichomes is important in the development of resistance against pathogens and pests in two species of tomato. We have used genetic and genomic approaches to uncover some of the biochemical and molecular mechanisms that underlie the divergence in trichome metabolism between the wild species Solanum habrochaites LA1777 and its cultivated relative, Solanum lycopersicum. LA1777 produces high amounts of insecticidal sesquiterpene carboxylic acids (SCAs), whereas cultivated tomatoes lack SCAs and are more susceptible to pests. We show that trichomes of the two species have nearly opposite terpenoid profiles, consisting mainly of monoterpenes and low levels of sesquiterpenes in S. lycopersicum and mainly of SCAs and very low monoterpene levels in LA1777. The accumulation patterns of these terpenoids are different during development, in contrast to the developmental expression profiles of terpenoid pathway genes, which are similar in the two species, but they do not correlate in either case with terpenoid accumulation. However, our data suggest that the accumulation of monoterpenes in S. lycopersicum and major sesquiterpenes in LA1777 are linked both genetically and biochemically. Metabolite analyses after targeted gene silencing, inhibitor treatments, and precursor feeding all show that sesquiterpene biosynthesis relies mainly on products from the plastidic 2-C-methyl-d-erythritol-4-phosphate pathway in LA1777 but less so in the cultivated species. Furthermore, two classes of sesquiterpenes produced by the wild species may be synthesized from distinct pools of precursors via cytosolic and plastidial cyclases. However, highly trichome-expressed sesquiterpene cyclase-like enzymes were ruled out as being involved in the production of major LA1777 sesquiterpenes.     

Molecular characterization and diversity of the Pina and Pinb genes in cultivated and wild diploid wheat

Grain hardness is one of the most important characteristics of wheat quality. Soft endosperm is associated with the presence of two proteins in the wild form, puroindoline a and b. The puroindoline genes and their derived proteins are present in the putative wheat diploid ancestors which are thought to be the donors of the A, B and D genomes in common and durum wheat. In this study, we investigated the variability of grain hardness in einkorn, along with the nucleotide diversity of Pina and Pinb genes in a collection of einkorn wheat and T. urartu, in addition to studying the neutrality and linkage disequilibrium of these genes. Various alleles were detected for Pina and Pinb genes including three novel alleles for the Pinb locus: Pinb-A ^m 1i, Pinb-A ^m 1j and Pinb-A ^m 1k. Some differences were found in grain hardness between the different genotypes. The neutrality test showed a different pattern of variation between the two Pin genes. The genetic analysis of a diploid wheat collection has demonstrated that these species are a potential source of novel puroindoline variants. Our data suggest that, although further studies must be carried out, these variants could be used to expand the range of grain texture in durum and common wheat, which would permit the development of new materials adapted to novel uses in the baking and pasta industry.     

Variation in cellular ribulose-1,5-bisphosphate-carboxylase content in leaves of Triticum genotypes at three levels of ploidy

Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 1.1.39) (RuBPCase) was quantified using polyacrylamide-gel electrophoresis in whole 9-d-old first leaves of 14 genotypes of Triticum, and cellular RuBPCase levels calculated. Diploids, tetraploids and hexaploids were analysed and it was confirmed that the RuBPCase level per cell is closely related to ploidy in wheat. Inter-genotypic variation in RuBPCase levels per cell and per leaf were surveyed. It was found that the interactions between leaf size, cell size and RuBPCase levels result in small variations in RuBPCase levels per unit leaf area between genotypes.Abbreviation RuBPCase ribulose-1,5-bisphosphate carboxylase/oxygenase     

The plant-like C2 glycolate cycle and the bacterial-like glycerate pathway cooperate in phosphoglycolate metabolism in cyanobacteria

The occurrence of a photorespiratory 2-phosphoglycolate metabolism in cyanobacteria is not clear. In the genome of the cyanobacterium Synechocystis sp. strain PCC 6803, we have identified open reading frames encoding enzymes homologous to those forming the plant-like C2 cycle and the bacterial-type glycerate pathway. To study the route and importance of 2-phosphoglycolate metabolism, the identified genes were systematically inactivated by mutagenesis. With a few exceptions, most of these genes could be inactivated without leading to a high-CO(2)-requiring phenotype. Biochemical characterization of recombinant proteins verified that Synechocystis harbors an active serine hydroxymethyltransferase, and, contrary to higher plants, expresses a glycolate dehydrogenase instead of an oxidase to convert glycolate to glyoxylate. The mutation of this enzymatic step, located prior to the branching of phosphoglycolate metabolism into the plant-like C2 cycle and the bacterial-like glycerate pathway, resulted in glycolate accumulation and a growth depression already at high CO(2). Similar growth inhibitions were found for a single mutant in the plant-type C2 cycle and more pronounced for a double mutant affected in both the C2 cycle and the glycerate pathway after cultivation at low CO(2). These results suggested that cyanobacteria metabolize phosphoglycolate by the cooperative action of the C2 cycle and the glycerate pathway. When exposed to low CO(2), glycine decarboxylase knockout mutants accumulated far more glycine and lysine than wild-type cells or mutants with inactivated glycerate pathway. This finding and the growth data imply a dominant, although not exclusive, role of the C2 route in cyanobacterial phosphoglycolate metabolism.     

Variation of total soluble seminal root proteins of tetraploid wild and cultivated wheat induced at cold acclimation and freezing

The relationship between total soluble seminal root proteins induced at cold acclimation and freezing tolerance in tetraploid wild wheat Aegilops L. (Ae. biuncialis, Ae. cylindrica) and cultivated wheat Triticum turgitum L. (Firat-93, Harran-95) was investigated. Cold acclimation was performed at 0 °C for 7 days. Freezing tolerance was determined with survived roots after freezing treatments at −5 and/or −7 °C for 3, 6, 12 and 24 h. At −5°C, all tetraploid genotypes showed over 60% tolerance for 3 h. This effect was also present in wild wheat for 6 h, but was decreased in cultivated wheat to 30–35% tolerance for 6 h. Only Ae. biuncialis was able to show 52% tolerance just for 3 h freezing period at −7 °C. However, all the genotypes were not survived at −7 °C, for 6, 12 and 24 h. Cold acclimation induced greater amounts of new soluble seminal root proteins in tolerant Ae. biuncialis (29–104 kDa, pI 5.4–7.4) than in sensitive Harran-95 (29–66 kDa, pI 6.1–8.3). Synthesis and accumulation of these proteins may be related to degree of freezing tolerance of these genotypes.     

Effect of glycidate, an inhibitor of glycolate synthesis in leaves, on the activity of some enzymes of the glycolate pathway

Under conditions where glycolate synthesis was inhibited at least 50% in tobacco (Nicotiana tabacum L.) leaf discs treated with glycidate (2,3-epoxypropionate), the ribulose diphosphate carboxylase activity in extracts and the inhibition of the activity by 100% oxygen were unaffected by the glycidate treatment. [1-¹⁴C]Glycidate was readily taken into leaf discs and was bound to leaf proteins, but the binding occurred preferentially with proteins of molecular weight lower than ribulose diphosphate carboxylase. Glycidate added to the isolated enzyme did not inhibit ribulose diphosphate carboxylase activity or affect its inhibition by 100% O₂. Thus, glycidate did not inhibit glycolate synthesis by a direct effect on ribulose diphosphate carboxylase/oxygenase.     

Photosynthetic capacity and carbon allocation patterns in diverse growth forms of Eucalyptus

Summary Eucalytptus species originating in Australian habitats differing in moisture regimes were examined under uniform growth conditions for their photosynthetic characteristics and allocation patterns. Species from the driest environments, the mallee types, had the smallest leaf sizes and the highest leaf specific weights; and forest species, from moist coastal sites, had the largest and thinnest leaves. Photosynthetic rates on a dry weight basis were highly correlated with leaf nitrogen content in all species. Leaf nitrogen content on a dry weight basis varied little between species in nature; however, there were increasing amounts of nitrogen per unit leaf area as the habitat became drier because of the changes in specific leaf weight. This resulted in a greater light-saturated photosynthetic rate per leaf area of arid habitat species, which were presumably more efficient in water use as a consequence. A simple simulation model showed that changes in the allocation ratio to leaf weight reduces total leaf area in the expected direction without affecting total dry matter accumulation.     

Selectivity of diclofop-methyl between wheat and wild oat: growth and herbicide metabolism

Abstract Growth of the second leaf of susceptible wild oat (Avena fatua L.) was inhibited within 2 days after treatment with the herbicide, diclofop-methyl, in the 1-1/2 leaf stage. Leaf growth of resistant wheat (Triticum aestivum L.) was unaffected by diclofop-methyl. In wild oat. chlorosis developed 1 day after leaf growth was inhibited. Foliar absorption of diclofop-methyl was similar between wild oat and wheat with 67 and 61% of the recovered radioactivity from [¹⁴C]diclofop-methyl being absorbed by wild oat and wheat, respectively, after 4 days. Wild oal was equally sensitive to the methyl ester and acid forms of the herbicide when the compounds were injected into the stem. Wheat was unaffected by both forms when treated similarly. Very little diclofop-methyl and diclofop (combined total of 10 to 12% in wild oat and 5 to 7% in wheat) remained in plant tissues 2 days after leaf treatment in both susceptible and resistant plants. Therefore, the active form of the herbicide must inhibit growth of susceptible plants very rapidly and at relatively low concentrations. Diclofop-methyl was rapidly hydrolyzed to diclofop by wild oat and wheat. Wild oat predominantly conjugated diclofop to an ester conjugate but wheat hydroxylated the 2,4-dichlorophenyl ring and formed a phenolic conjugate. The formation of the different conjugates between wild oat and wheat was the most significant difference in metabolism between the two species. Nearly 60 and 70% of the methanol-soluble radioactivity was present as water-soluble conjugates in wild oat and wheat, respectively, 4 days after treatment.     

Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants

Summary An experiment was conducted to determine whether wild accessions and cultivars ofLycopersicon esculentum Mill. differed in inherent morphological, physiological or phenological traits and whether such differences would result in variation in response to vesicular-arbuscular mycorrhizal infection. While distinctions between wild accessions and cultivars were apparent (the cultivars generally had higher phosphorus use efficiencies and shorter lifespans than the wild accessions) and the cultivars were, as a group, more responsive to mycorrhizal infection than the wild accessions, there was significant variation among wild accessions and among cultivars in response to infection. Regardless of cultivation status, non-mycorrhizal plant root density was significantly negatively correlated with response to infection. Phosphorus use efficiency was generally not significantly correlated with response to infection. Mycorrhizal infection decreased phosphorus use efficiency in all accessions, but had variable effects on root density, depending upon accession and time. Finally, the vegetative response was not necessarily of the same magnitude as the reproductive response.     

Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants

Summary We tested the hypothesis that mycorrhizal infection benefits wild plants to a lesser extent than cultivated plants. This hypothesis stems from two observations: (1) mycorrhizal infection improves plant growth primarily by increasing nutrient uptake, and (2) wild plants often possess special adaptations to soil infertility which are less pronounced in modern cultivated plants. In the first experiment, wild (Avena fatua L.) and cultivated (A. sativa L.) oats were grown hydroponically at four different phosphorus levels. Wild oat was less responsive (in shoot dry weight) to increasing phosphorus availability than cultivated oat. In addition, the root: shoot ratio was much more plastic in wild oat (varying from 0.90 in the low phosphorus solution to 0.25 in the high phosphorus solution) than in cultivated oat (varying from 0.44 to 0.17). In the second experiment, mycorrhizal and non-mycorrhizal wild and cultivated oats were grown in a phosphorus-deficient soil. Mycorrhizal infection generally improved the vegetative growth of both wild and cultivated oats. However, infection significantly increased plant lifespan, number of panicles per plant, shoot phosphorus concentration, shoot phosphorus content, duration of flowering, and the mean weight of individual seeds in cultivated oat, while it had a significantly reduced effect, no effect, or a negative effect on these characters for wild oat. Poor positive responsiveness of wild oat in these characters was thus associated with what might be considered to be inherent adaptations to nutrient deficiency: high root: shoot ratio and inherently low growth rate. Infection also increased seed phosphorus content and reproductive allocation.